THISTLEWOOD, ARTHUR (1770-1820), the principal instigator of the Cato Street conspiracy, a plot formed to murder the British cabinet in 1820. A son of William Thistlewood, and born at Tupholme in Lincolnshire, young Thistlewood became a soldier and visited France and America. He developed republican sympathies and on taking up his residence in London joined the Spencean Society, a revolutionary body ; associated himself with James Watson (d. 1838) and other agitators; and in December 1816 helped to arrange a meeting in Spa Fields, London, which was to be followed by the seizure of the Tower of London and the Bank of England, and by a general revolution. The proposed rising failed, but the Habeas Corpus Act was suspended and Thistlewood and Watson were tried but acquitted. Thistlewood continued his intrigues and was sentenced to a year's imprison ment for challenging the home secretary, Lord Sidmouth, to a duel. After his release in May 1819, having broken away from Henry Hunt and the more moderate reformers, he prepared a new and comprehensive plot. On Feb. 23, 182o, at a time of
great distress and during the unrest caused by the death of George III., the cabinet ministers had arranged to dine at the earl of Harrowby's house in Grosvenor Square. With some associ ates Thistlewood hired a room in the neighbouring Cato Street, collected arms and made ready to fall upon Harrowby's guests.
The authorities had been informed of the plot, probably by one of the conspirators named George Edwards ; officers appeared upon the scene and arrested some of the conspirators; and al though Thistlewood escaped in the confusion he was seized on the following day. Tried for high treason, Thistlewood and four others were sentenced to death, and were hanged on May I, 1820. See Sir S. Walpole, History of England (189o), vol. i.